Added score_only option.

[tcaceresm]

Summary

This adds a score_only function to MetalDock that evaluates docking scores of input pose without performing any local or global searches. The workflow remains the same.

Why

Useful when working with different conformations of same ligand and receptor (for example, conformations sampled using MD simulations).

Requirements

As usually, requires a ligand.xyz, a receptor.pdb and an input file. Inside input file, in [DOCKING] section, score_only = True must be set.

Limitations

Single-point calculations are still required to derive the partial charges of the atoms, which is relatively slow. However, there is a workaround: perform the single-point calculation once and then reuse the QM output in subsequent calculations for the same ligand (but with a different conformation).

Misc

This is my first PR ever. Feel free to give any opinion.